In general, the archer and the archery tackle, that is the bow, arrow, release mechanism, arrow rest, and bow sight, are viewed as a bow system. With respect to archery physics, bow system consistency is the fundamental component in highly accurate shooting. Measuring arrow dynamics in the bow system is a superior way to detect and improve performance. As those skilled in the art are filly aware, minute deviations in archery tackle setup or variations in hand position during arrow release degrade bow system accuracy. When an arrow is released from the bow system, vertical and horizontal bending moments are always induced in the arrow shaft. The trajectory of an arrow is dynamically stable and contains damped sinusoidal bending moments or oscillations in both vertical and horizontal planes along the longitudinal axis of the arrow. These oscillations occur due to asymmetric forces exerted upon on the bow string which thereby imparts comparable forces on the arrow. Any force exerted upon the arrow shaft that causes position deviations during arrow flight increases the size of the arrow impact area or produces larger arrow groups. A properly tuned bow system will minimize these asymmetric forces. Therefore, at a given distance, a properly tuned bow system, a combination of both archer and archery tackle, will produce minimal arrow group geometry.
One such example of accuracy degradation would pertain to the stiffness of the arrow or arrow spine. For any bow system, improperly spined arrows will produce horizontal oscillations with increasing amplitude; thus increasing arrow group width and reducing bow system accuracy. These horizontal oscillations can occur from arrows that are either too stiff or too flexible. Another example of an improperly tuned bow system would relate to arrow position on the bow string. An arrow is coupled to the bow string with an arrow nock that mechanically grips the string. Reproducible arrow placement upon the bow string is achieved with a nock set. The nock set is a device the archer permanently attaches to the bow string that enables the archer to place the arrow nock at the same point on the bow string each time an arrow is to be released. If the nock set is placed too high or too low, tremendous vertical oscillations will result, thus producing vertical elongation of the arrow group and reducing bow system accuracy. Yet another example is the improperly timed cams on a compound bow. Compound bows are characterized by a wheel and cable system integral to the limbs of the bow. As the bow is drawn, the wheel and cable system provides a mechanical advantage or leverage on the bow limbs; thus reducing the force required to hold the limbs at full draw by as much as 70%. As I understand it, a compound bow is synchronized when both wheels rotate an equal number of degrees at full draw. If the wheels are not synchronized, an effect very similar to an improper nock set location is realized. Arrow groups will elongate and decrease the accuracy of the bow system.
Previously, archery tackle performance was primarily determined by measuring arrow velocity in close proximity to the bow system or measuring arrow group geometry of the target face. Prior Art illustrates that arrow velocity was determined by placing a complex mechanical apparatus adjacent to a stationary target. One such invention is described in U.S. Pat. No. 3,401,334. To measure arrow velocity, a moveable target released from the apparatus would fall in the arrow path down the surface of the stationary target. As the arrow strikes the stationary target, the moving target is pinned to the stationary target. By knowing the moveable target's relationship with respect to gravity, the measured distance it fell, and the distance the arrow traveled, arrow velocity could be calculated. With consideration to determining archery tackle performance, this method is inaccurate since the falling target must be released at the precise moment the arrow is loosed from the bow. Any attempt to couple an electromechanical triggering device to the bow limb changes shot dynamics and will not deliver actual bow system performance. Additionally, critical data with respect to arrow motion or position at the moment of arrow release has dissipated significantly if the measurement apparatus is not intimately coupled to the bow.
As the state of the art in electronics advanced, independent or stand-alone chronographs were developed to measure transit time of a moving projectile. One such invention is described in U.S. Pat. No. 4,574,238. This alternate method utilizes an independent electronic chronograph to measure projectile velocity. As I understand it, photoelectric devices use ambient light or incandescent light to detect the projectile "shadow" as it passes along a predetermined measuring path through the two-stage chronograph window. An electronic circuit calculates projectile velocity based upon the "shadow" transit time and the known length of the chronograph window. As with the first technique, arrow velocity can only be conveniently measured when the arrow is released with the measuring device placed in front of the bow system, thereby eliminating collection of critical data pertaining to initial arrow motion or position.
This present invention provides the archer with the capability of quantifying the arrow position during its most critical point of travel: traversing the bow riser. With intimate mounting to the bow, the present invention delivers data on arrow dynamics not available with prior state-of-the-art designs.